1. Field of the Invention
The light source with a WDM function according to the present invention relates to a light source device having the function of wavelength-multiplexing a plurality of lights. The light source device according to the present invention is applicable to an optical communications device and an optical information processing device, and furthermore to an optical fiber amplifier and a two-way optical transmission apparatus can be applied to an optical communication field.
2. Description of the Related Art
An optical repeater for amplifying a signal light attenuated in a transmission line fiber is used in a long-distance optical fiber communications system. As an optical repeater, an optical fiber amplifier for directly amplifying the signal light using a rare-earth doped optical fiber as a gain media is well known.
In the optical fiber amplifier, it is necessary to lead with a signal light a pump light to a rare-earth doped optical fiber for use in an optical amplifying operation by exciting a rare-earth doped optical fiber. To attain this, the optical fiber amplifier should be designed to include a wavelength division multiplexer (WDM coupler) for division-multiplexing the signal light and the pump light.
That is, the conventional optical fiber amplifier includes a pump light source for outputting a pump light; a WDM coupler for division-multiplexing a pump light and a signal light and leading the resultant light to a rare-earth doped optical fiber; and a rare-earth doped optical fiber, that is, a gain media. For example, an optical fiber fused coupler and an optical filter made of a dielectric multi-layered film can be used as a WDM coupler.
In the conventional optical fiber amplifier, the optical coupler for coupling a pump light source with an optical fiber and a WDM coupler are arranged after being inserted into the optical path from the pump light source to a rare-earth doped optical fiber. Therefore, the output of the pump light source is attenuated by the optical coupler and the WDM coupler. As a result, the pump light power input to the rare-earth doped optical fiber is reduced. This causes such a disadvantage that the gain of the signal light in the rare-earth doped optical fiber is undesirably reduced.